In consideration of the future of the environment, there has recently been much attention focused on environmentally friendly electric vehicles, and research and development focused on electric vehicles has consequently been carried out by automobile manufacturers and the like.
Battery design and R&D is focused on electric vehicles that include features such as internal batteries, receive power from an external source when the batteries require charging, and convert the electrical energy stored in the batteries to mechanical force to drive the vehicles.
However, electric vehicles that have been developed to date, in terms of battery efficiency, have had difficulty traveling beyond a distance of about 200 km on a single (full) charge.
As a method of overcoming this limited travel range accompanying a single-charge, research into lightening the body or underbody of an electric vehicle, in order to increase the travel range thereof, has been conducted.
For example, there have been efforts in the related art to lighten an underbody by replacing the underbody material with plastic or aluminum, or making certain portions of a steel underbody high-strength, in order to reduce the material thickness and achieve lighter weight.
However, when plastic materials or aluminum are used in the related art, a significantly greater amount of CO2 is discharged throughout the overall product life, from manufacturing to recycling. In particular, in the case of plastic used in a body, it may be difficult to recycle, its strength is difficult to maintain, and its cost is high, as compared to steel.
Also, in related art inventions, in which portions of a steel material underbody are made high-strength to reduce material thickness, there is the limitation of an overall reduction in underbody strength against bending and twisting.
Ultimately, a reduction in underbody strength against bending and twisting fundamentally results in deteriorated ride quality and handling of an electric vehicle.
Another technique for increasing the travel range of an electric vehicle is to enable a battery mounted (installed) in an electric vehicle to be easily replaceable at a service station or other facility.
However, while not shown in a separate drawing, most related art electric vehicles have structures in which the battery must be entirely replaced, which requires the use of a car hoist to raise the vehicle and replace the battery or a facility that allows the battery to be replaced from a recess in the ground below the vehicle.
Currently, the replacement of an electric vehicle battery requires complex equipment and cannot be easily performed by a vehicle driver.
Also, even if a desired travel distance is 100 km or less after charging an electric vehicle, all batteries must be mounted and completely charged for use, which involves having to mount and carry more batteries than necessary.
In instances in which electric vehicles are used for commuting, even in the case that a battery charge capacity is only required for short range travel, because a battery (pack) must always be carried in a conventional electric vehicle, this gives rise to the limitation of reduced travel efficiency as a result of more electricity consumed in order to overcome the greater load from the increased weight of the vehicle.